1. Field of the Invention
The present invention is generally in the field of semiconductors. More particularly, the invention is in the field of fuses in semiconductor dies.
2. Background Art
Fuses, for example, fuses that can be blown by a laser (“laser fuses”), can be utilized in integrated circuit (IC) dies to perform various functions such as, for example, providing redundancy in semiconductor memory, trimming, e.g., adjusting resistance or capacitance values in a circuit, and chip ID. Laser fuses, which can comprise a metal, such as copper, are typically formed in a high interconnect metal layer, such as a top interconnect metal layer, in the die and are covered by a thick dielectric layer. To enable the laser fuse to be blown by a laser, a fuse window can be formed by using an etch process to thin a portion of the dielectric layer overlying the laser fuse. The remaining portion of the dielectric layer overlying the laser fuse after formation of the fuse window must be sufficiently thin so as to allow laser fuse to be blown by the laser while providing adequate protection to the laser fuse.
However, due to an anomaly, the etch process may etch through the dielectric layer at, for example, an edge of the fuse window and expose the underlying fuse metal. As a result, an etch chemistry utilized in the etch process can attack the fuse metal and, thereby, damage to the laser fuse. For example, the etch chemistry may remove enough fuse metal so as to cause an unblown laser fuse to be in a blown condition. Thus, it is important to determine if the structural integrity of a laser fuse has been compromised by the etch process during fuse window formation.
In a conventional approach, fuse windows can be visually inspected during wafer fabrication to determine if underlying laser fuses have been compromised by the etch process. However, since a wafer may include hundreds of dies that can each include, for example, as many as ten fuse windows, a visual inspection of each fuse window is not feasible. Thus, the conventional approach typically employs a spot inspection, wherein only some of the fuse windows in some of the dies on the wafer are randomly inspected. However, since different areas of the wafer may etch at different rates, some dies on the wafer may have fuse windows with defects that can compromise an underlying laser fuse while other dies on the wafer may have fuse windows that are defect free. Thus, the spot visual inspection provided by the conventional approach may not detect defective fuse windows on some dies. Also, the conventional approach may not be sensitive enough to detect minor laser fuse damage, which can undesirably affect the integrity and reliability of the laser fuse.